Piezoelectric ceramics

ABSTRACT

A CERAMIC HAVING EXCELLENT PIEZOELECTRIC AND DIELECTRIC CHARACTERISTICS OBTAINED FROM A COMPOSITION OF   PB((ZN1/3NB2/3)XTIYZRZ)O3   WHEREIN X+Y+Z=1. THE PIEZOELECTRIC CERAMIC HAS A HIGH CURIE POINT, IMPROVED PIEZOELECTRIC CHARACTERICTICS AS COMPARED WITH THE CONVENTIONAL BATIO3 CERAMICS, HAS GOOD INSULATION RESISTANCE, AND IS EASY TO SINTER AS COMPARED WITH PB(ZRTI)O3 CERAMICS, THEREBY BEING VERY USEFUL IN THE INDUSTRY. THE RADICAL COUPLING CONSTANT OF THE CERAMIC CAN BE INCREASED BY INCLUDING AN ADDITIVE OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF NA2CO3, CU2O, AG2O, MGO, NIO, FE2O, IN2O, IN2O3, SNO2, CR2O3 AND CO2O3 IN A TOTAL QUANTITY UP TO 5 MOL PERCENT OF THE COMPOSITION OR AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF CACO3, SRCO3, AND BACO3 IN A TOTAL QUANTITY UP TO 10 MOL PERCENT OF THE COMPOSITION.

United States Patent Office 3,741,899 Patented June 26, 1973 3,741,899PIEZOELECTRIC CERAMICS Akio Koyano, Mishima, Japan, assignor to SumitomoSpecial Metal Company Limited, Osaka, Japan Confinuation-in-part ofabandoned application Ser. No. 713,081, Mar. 14, 1968. This applicationDec. 16, 1970, Ser. No. 98,650

Claims priority, application Japan, Mar. 16, 1967, 42/16,516; Aug. 25,1967, 42/54,660; Nov. 2, 1967, 42/70,734

Int. Cl. C04b 35/46, 35/48 US. Cl. 252-623 6 Claims ABSTRACT OF THEDISCLOSURE A ceramic having excellent piezoelectric and dielectriccharacteristics obtained from a composition of wherein X+Y+Z=L Thepiezoelectric ceramic has a high curie point, improved piezoelectriccharacteristics as compared with the conventional BaTiO ceramics, hasgood insulation resistance, and is easy to sinter as compared with Pb(ZrTi.) ceramics, thereby being very useful in the industry. The radialcoupling constant of the ceramic can be increased by including anadditive of at least one member selected from the group consisting ofNa2C03, C11 0, Ag O, F620, 111203, S1102, Cr O and C0 0 in a totalquantity up to mol percent of the composition or at least one memberselected from the group consisting of CaCO SrCO and BaCO in a totalquantity up to mol percent of the composition.

This is a continuation-in-part application of my copending applicationSer. No. 713,081, filed Mar. 14, 1968, and now abandoned.

This invention relates to the ternary solid solution system of and itsobject is to obtain novel and improved piezoelectric ceramics.

Barium titanate and lead titanate-lead zirconate or lead titanate-leadzirconate-lead titanate ceramics have been and that, when PbZrO andvarious kinds of additive elements are also added to the above mentionedbinary solid solution ceramics, the piezoelectric characteristics areimproved. 1

In the accompanying drawings:

FIGS. 1, 2, 3 and 4 are diagrams showing a radial electro-mechanicalcoupling constant and a dielectric constant of ceramic compositionaccording to the present invention; and

FIG. 5 is a diagram showing a' temperature variation of an insulatingresistance.

The present invention provides piezoelectric ceramics which are easy tosinter and which have improved piezoelectric and dielectriccharacteristics by limiting'the com- I position within a polygonalregion ABCDEF as shown in FIG. 3, the basic composition formula beingrepresented by Pb 1/3 2/3)X Y 'z 3 wherein X+Y+Z=1, and X 0.01.

It is considered to be very difficult to sinter lead compounds suchaslead titanate zirconate, because as lead oxide is evaporated at asintering stage, uniform ceramics are hard to obtain. On the other hand,according to the present invention, uniform and compact ceramics can beeasily obtained.

For instance, in the case of X =0 in the basic composition, as wellknown, the sintering process is usually carried out at 1250 to 1300 C.in a PbO atmosphere in order to prevent the evaporation of PbO, butuniformity is not maintained and good ceramics are not obtained easily.Especially when X =0 and Z =0, the sintering process is so difficultthat useful ceramics cannot be obtained.

But by the increase of the amount of X, the solidus line is lowered andconsequently the sintering proceeds at a low temperature so that uniformand compact ceramics are obtained.

For example, in the case of X :05, the optimum sintering temperature isabout 1100 C. and favorable piezoelectric and dielectric characteristicsare obtained. In view of the fact that generally the evaporation of Pb Oquickly increases above about 1200 C., the materials according to thepresent invention are more easy to sinter than the other ceramics suchas lead titanate zirconate. Particularly in a range of X 0.5 theevaporation of PhD is negligible because the sintering temperature islower than 1100 C. This is very useful to the piezoelectric ceramicsindustry.

Furthermore, the piezoelectric ceramics are generally used in the stateof residual polarization. Accordingly, a high insulating resistance isrequired to obtain a saturation polarization and a high dielectricstrength is required to prevent a break-down in the polarization stage.For this requirement the present ceramics have an insulating resistanceof more than 10 n-cm. and a dielectric strength of more than 50 kv./cm.at C. Therefore they overcome the above mentioned difficulties.

Here, the complex compound of should only be discussed in the solidsolution with PbTiOg and/or PbZrO because on the basis of synthesizingtheory it has a possibility of forming a perovskite structure anddoesnot tend to assume a single phase by itself.

wherein X +Y=1, PbO, ZnO, Nb O and TiO each having high purity, andmixed in proper portion. The mixture was then calcined at 750 C. in therange of X5035 and at 850 C. in the range of X 0L35 and thereaftercrushed; The crushed mixture was pressed to form disks, each of whichwas 13 mm. in diameter and 2 mm. thick. The disks were then sintered,respectively, at a required temperature for one hour. The optimumsintering temperature was difierent depending on the respectivecompositions and lowered with the increase of X, as shown in Table 1,due to the lowering of the X solidus line with the increase of X.Therefore, it was not desirable to considerably exceed the optimumtemperature shown in Table 1. For example, the sintering temperature washigher by 100 C. than shown in Table 1; the sample was deformed. Afterthe sample was sintered, a silver electrode was fired on each surface ofthe disk and a direct current field of 50 kv./cm. was applied for 5minutes in an oil bath at 100 C. to polarize the sample. In 24 hoursafter polarization, the measurement was carried out.

The results are shown in FIGS. 1, 2, 3, and 4 and the typical examplesof them are shown in Table 1.

TAB LE 1 Radial Sintering Sintering coupling Curie Ex. Compotemp.density Dielectric constant mp. N o. sition X C.) (gnlcrnfi) constant(percent) C.)

a As evident from Table l and FIGS. 3 and 4, improved ceramics havingdesirable piezoelectric and dieleptric characteristics were obtained ata low sintering temperature where PbO evaporation is negligibly small.In practice, the value of Kr of the piezoelectric ceramic material isrequired to be more than 10%. This requirement can be satisfied byselecting the composition of the applicants invention in a range of0.3X0.9.

Further, in a range of 0.5X S 0.89 a value of Kr of more than 20% can beobtained. Particularly, in the range of 0.5X0.89, not only favorablepiezoelectric characteristics can be obtained, but also the optimumsintering temperature is lower than 1100 C. as above mentioned so thatthe PbO evaporation may practically be negligible. This is very usefulin the industry, as compared with the conventional PbTiO --PbZrO3ceramics.

EXAMPLE 2 In a composition wherein PbZrO is also solid dissolved in thebasic composition disclosed in Example 1:

wherein X +Y+Z=1, the same treatment as described in Example 1 wasapplied varying the amounts of X, Y and Z.

The results are shown in FIGS. 3 and 4 and the typical examples of themare shown in Table 2. Some examples of the temperature variation of theinsulating resistance are shown in FIG. 5.

The reference numerals given in FIG. indicate the composition of therespective sample numbers shown in Table 2.

TABLE 2 Radial Composition sintering sintering coupling Ex: temp.density Dielectric constant No.- X Z C.) (grJemJ) constant (percent) Thepolarization was carried out at 50 kv./cm. for 5 minutes in the samemanner as in Example 1 in the range of X 20.01. When X 0.0l, takingquick reduction of the breakdown voltage and insulating resistance intoconsideration, a direct current field of 40 kv./cm. was applied forhours.

As can be seen from Table 2, the piezoelectric characteristics werefurther improved by the dissolution of PbZrO in the binary system of andits elfects are more definitely shown in FIGS. 3 and 4. Thus, as theresult of further addition of PbZrO to the above mentioned binary solidsolution ceramics in the range of X505 a good sinterability can bemaintained, the sintering process at a low temperature of lower thanabout 1100" C., and the piezoelectric characteristics are furtherimproved in the state wherein a favorable dielectric characteristic ismaintained.

As mentioned above and as shown in FIG. 5, the insulating resistance ofthe ceramics of the present invention is extremely high at hightemperature. This is desirable from the industrial viewpoint consideringthe fact that the polyarization has been carried out at such a hightemperature as C. to 200 C. to complete it within a short time.

EXAMPLE 3 In the basic composition formula Pb (Zl'l1 Nb Ti Z1'zO whereinX Y+Z=1, the experiment was carried out in the same manner as in Example2 with the addition of a small amount of the additives. Said additiveswere selected from less than 10 mol percent of CaCO SrCO BaCO and lessthan 5 mol percent of Na CO GU30, Ag O, MgO, (31 203, C0203, PC2033,111203 and S1102- In this experiment the raw materials were prepared byusing all of Ca, Sr, Ba and Na in the form of carbonates. The carbonatesof these elements were used only because they are readily obtainedcommercially. Accordingly, the raw material to be used in the presentinvention is not limited to the carbonates and can be replaced by allcompounds such as hydroxides which become oxides when baked and have thesame eifect as the carbonate.

As evident from Table 3, by the addition of less than 10 mol percent ofCaCO SrCO or BaCO or less than 5 mol percent of Na CO Cu O, Ag O, MgO,NiO, Cr O Fe O In 0 or SnO the radial coupling coefiicient anddielectric constant are increased. 1

When the amount of the additive exceeds 10 mol percent of CaCO SrCO andBaCO and 5 mol percent of the others, the insulating resistance dropswhereby at the time of polarization the leakage current increases or theinsulating breakdown occurs.

As disclosed in Example 3, it is found that the piezoelectriccharacteristics are further improved by adding PbZrO and the slightamount of additive element to Pb(Zn Nb )O-PtTiO ceramics. It isgenerally preferable that the value of Kr is relatively high. However,various values of more than 10% are required according to practicalusage. Such requirements can be satisfied by selecting the mixedcomposition in compliance with FIG. 3. The composition according to thepresent claim is defined to be within the polygonal region ABCDEF inFIG. 3, in the region of which the value of Kr is more than 10%. Asaforementioned outside the line CD uniform and compact ceramics cannotbe obtained easily and the insulating resistance is lowered so thatpolarization may be difiicult to be carried out. And outside the linesBC, and ED the value of Kr becomes lower than 10%, the Ivalue of whichbeing hardly usable and furthermore, outside the line FA inferiorceramics are obtained and Kr becomes less than 10%.

The points A, B, C, D, E and F are represented by the followingcompositions:

X Y Z novel and improved piezoelectric ceramics can be obtained. Morespecifically, by increasing the amount of 1 and 2, both the relativecoupling constant and dielectric constant peak where the amount of Pb(Zn Nb )O is .84 (X=0.84). This is a result unknown to the prior artwhich has utilized a piezoelectric ceramic composition of essentiallythe same elements as applicants composition, but with differentquantities of Pb(Zn Nb )O PbTiO and PbZrO Radial Mechanical Basiccomposition Smtenng coupling quality M01 temp. Dielectric constantfactor Ex. No X Z Additive percent C.) constant percent (Qm) 0. 84 9802, 109 43.2 99 0. 84 0 2 980 3, 062 51. 3 83 0. 84 0 2 980 2, 450 52. 680 0. 84 0 2 980 2, 821 54. 0 78 0. 84 0 2. 980 2, 715 50. 2 81 0. 84 02. 5 980 2, 291 50. 7 80 0. 84 0 2. 5 980 2, 650 49. 8 97 0. 84 0 3 9802, 630 50. 3 79 0.84 0 2 980 2, 483 51. 1 79 0.84 0 1 980 2, 399 52. 3210 0. 84 0 1 980 2, 110 53. 3 680 0. 84 0 2 980 2, 970 58. 6 87 .0. 840 1 980 2, 430 52. 1 89 0. 84 0 p 2 980 2, 709 55. 6 79 0. 625 0. 16None 1, 080 2, 278 57.0 83 0. 625 0. 16 2 1, 080 2, 748 67. 3 81 0. 6250. 16 1. 5 1, 080 2, 480 60. 7 80 0. 625 0. 16 2 1, 080 2, 698 64. 4 760. 625 0. 16 V 2. 5 1, 080 3, 324 60. 2 72 0.625 0. 16 2. 5 1, 080 3,720 62.6 72 0. 625 0. 16 2. 5 1, 080 2, 900 61. 1 73 0.625 0. 16 2 1,080 2, 476 61. 5 80 0. 625 0.16 1 1,080 2,401 61.2 82

0. 625 0. 16 1 1, 080 2, 580 63. 7 130 0. 625 0. 16 1 1, 080 2, 024 61.0 625 0. 625 9. 16 1 1, 080 2, 916 68.7 79 0. 625 0. 16 1 1, 080 2, 61362. 6 120 0. 625 0. 16 1 1, 080 2, 599 64. 9 77 0. 375 0. 2 1, 150 90031. 1 91 0. 375 0. 2 3 1, 150 1, 415 40. 4 87 0. 375 0. 2 2 1, 150 1,611 43. 2 82 0. 375 0. 2 3 l, 150 1, 512 45. 3 83 0. 375 0. 2 5 1, 1501, 615 39. 6 76 0. 375 0. 2 5 1, 150 1, 620 41. 2 78 0. 375 0. 2 5 1,150 1, 311 38. 1 80 0. 375 0. 2 5 1, 150 1, 230 42. 8 81 p 0. 375 0.2 31, 150 1, 263 40. 3 83 0.375 0. 2 -2 1, 150 924 34. 8 590 0. 375 0. 2 51, 150 911 32. 0 1, 172 0. 375 O. 2 2 1, 150 827 36. 4 712 0. 375 0. 2 51, 150 653 29. 8 1, 214 0. 375 0.2 1 5 1, 150 1, 960 42. 6 87 0. 375 0.2 2 1, 150 1, 017 40. 6 316 0. 375 0. 2 5 1, 150 989 32. 7 528 0. 375 0.2 3 1, 150 1, 267 43. 7 80 0. 375 0. 315 1, 150 1, 463 61. 1 83 0. 3750. 315 1 1, 150 2, 432 6. 68 77 0. 375 0. 315 2 1, 150 2, 504 65. 8 770. 375 0. 315 1 1, 150 1, 940 65. 9 84 0. 375 0. 315 1 1, 150 1, 811 64.9 83 0. 375 0. 315 5 1, 150 2, 280 62. 7 80 0. 375 0. 315 5 1, 150 2,845 64. 8 80 0. 375 0. 315 5 1, 150 2, 120 64. 0 79 0. 375 0. 315 2.5 1,150 1. 683 63. 2 121 0. 375 0. 315 1 1, 150 1, 590 64. 3 99 0. 375 0.315 0. 5 1, 150 1, 579 68. 3 124 0. 375 0. 315 0. 5 1, 150 1, 252 65. 2156 0. 375 0. 315 2 1, 150 683 50. 0 811 0. 375 0. 315 1 1, 150 2, 23270. 7 75 0. 375 0. 315 0. 5 1, 150 1, 672 64. 2 118 0. 375 0.315 1 1,150 1, 788 66. 1 93 0. 375 0. 625 None 1, 150 590 15. 3 480 0. 375 0.625 4 1, 150 942 30. 2 296 0. 375 0. 625 3 1, 150 887 28. 7 340 0. 3750. 625 2 1, 150 942 36. 8 373 0.375 0. 625 4 1, 150 796 31. 1 315 0. 3750. 625 5 1, 150 1, 011 26. 3 280 0. 375 0. 625 5 1, 150 1, 220 30. 2 3050. 375 0. 625 5 1, 150 899 24. 6 313 0.375 0. 625 5 1, 150 746 31. 6 2970. 375 0. 625 5 1, 150 780 29. 7 399 0. 375 0. 625 2 1, 150 867 29. 9475 0. 375 0. 625 1 1, 150 815 31. 6 390 0. 375 0. 625 3 1, 150 610 27.8 788 0. 375 0. 625 2. 5 1, 150 926 30. 3 400 0.375 0. 625 5 1, 150 71129. 8 623 0. 375 0. 625 3 1, 150 1, 060 39. 2 411 0. 375 0.625 5 1, 150760 29. 6 423 0. 125 0. 45 1, 200 1, 438 59. 3 89 0. 125 0. 45 1 1, 2001, 987 64.9 82 0. 125 0. 45 1 1, 200 1, 780 65. 1 80 0. 125 0. 45 1 1,200 1, 921 65. 2 83 0. 125 0. 45 1, 200 2, 426 63. 7 78 0. 125 0. 5 1,200 2, 240 63. 5 79 0. 125 0.45 10 1, 200 2, 518 66. 1 0. 125 0.45 10 1,200 1, 963 62. 7 0. 125 0.45 2 1, 200 1, 872 64. 2 79 0. 125 0. 45 1 1,200 1, 713 63. 4 82 0, 125 0. 45 0. 5 1, 200 1, 580 64. 1 80 0. 125 0.450. 5 1, 200 1, 672 63. 8 99 0. 125 0. 45 1 1, 200 1, 899 64. 5 77 0. 1250.45 0. 5 1, 200 1, 716 63. 7 0. 0. 45 1 1, 200 1, 757 64. 6 81 What isclaimed is:

1. A piezoelectric ceramic composition consisting essentially of a solidsolution of a material of the form Pb (Zn Nb Ti Zr O where X +Y+Z=lhaving a composition within a polygonal region ABCDEF of FIG. 3 and anadditive of at least one member selected from the group consisting of NaCO Cu O, Ag O, MgO,NiO-, Fe O In O SnO Cr O and C 0 in a total quantityup to 5 mol percent of said'composition, said additive being present inan amount suflicient to increase the radial coupling constant of saidmaterial. 1

additive being present in an amount sufficient to increase the radialcoupling constant of said material.

5. A piezoelectric ceramic composition consisting essentially of a solidsolution of a material of the form Pb(Zn Nb Ti Zr 0 where X+Y+Z=1 havinga composition within a polygonal region LMNOP of FIG. 3 and an additiveof at least one member selected from the group consisting of Na COC1130, Ag O, MgO, NiO,

" 'Fe O' 11130 111203581103, crgog and C0 03 a total 2. A piezoelectricceramic composition consisting of esgroup consisting of CaCO SrCO andBaCO in a total quantity up to 10 mol percent of said composition, saidadditive being present in an amount sufficient to increase the radialcoupling constant of said material.

3. A piezoelectric ceramic composition consisting essentially of a solidsolution of a material of the form Pb(Zn Nb Ti Zr O where X+Y+Z=l havinga composition within a polygonal region GHIJK of FIG. 3 and an additiveof at least one member selected from the group consisting of Na CO Cu O,Ag O, MgO, NiO, Fe O 111303, SnO Cr O and C0 0 in a total quantity up to5 mol percent of said composition, said additive being present in anamount suificient to increase the radial coupling constant of saidmaterial.

4. A piezoelectric ceramic composition consisting essentially of a solidsolution of a material of the form Pb(Zl1 Nb2/3)xTiyZl'zo3 where X+Y+Z=1having a composition within a polygonal region GHIJK of FIG. 3

and an additive of at least one member selected from the groupconsisting of CaCO SrCO and BaCO in a total quantity up to 10 molpercent of said composition, said quantity up to 5 mol percent of saidcomposition, said additive being present in an amount suflicient toincrease the radial coupling constant of said material.

6. A piezoelectric ceramic composition consisting essentially of a solidsolution of a material of the form Pb(Zn Nb Ti Zr O where X+Y+Z=1 havinga composition within a polygonal region LMNOP of FIG. 3 and an additiveof at least one member selected from the group consisting of CaCO SrCOand BaCO; in a total quantity up to 10 mol percent of said composition,said additive being present in an amount sufiicient to increase theradial coupling constant of said material.

, References Cited UNITED STATES PATENTS 3,403,103 9/1968 Ouchi et a1.25262.9 3,068,177 12/1962 Sugden 25262.9 3,219,583 11/1965 Cook 25262.93,424,686 1/1969 Ouchi et al. 25262.9 3,546,120 12/1970 ,Ouchi et al.25262.9 3,268,453 8/1966 Ouchi et a1 25262.9

OTHER REFERENCES Veda et al.: Japanese Journal of Applied Physics, vol.7, No. 3, pp. 236-42, March 1968.

OSCAR R. VERTIZ, Primary Examiner J. COOPER, Assistant Examiner

